qseecom: correct range check in __qseecom_update_cmd_buf_64

Make change to validate if there exists enough space to write a
uint64 instead of a unit32 value, in __qseecom_update_cmd_buf_64.

Change-Id: I861cbada8f472123b5058511764b487281ae1343
Signed-off-by: Zhen Kong <zkong@codeaurora.org>